Rolling magnesium-base alloys



Patented Mar. 16 1943 ROLLING MAGNESIUM-BASE ALLOYS John 0. McDonald, Midland, Mich, assignor to The Dow Chemical Company, Midland, Mich., a corporation of Michigan No Drawing. Application April 21, 1941,

- Serial No. 389,601

6 Claims.

This invention relates to an improved method of producing rolled articles from magnesiumbase alloys. It is particularly applicable to rolling those alloys containing at least 85 per cent of magnesium together with a minor proportion I of one or more of the alloying elements aluminum, manganese, zinc, calcium, cadmium, cerium, silver, and silicon, and to other like alloys having suflicient ductility to permit substantial deformation.

Conventional methods of rolling magnesiumbase alloys are successful in producing articles of either high strength or high ductility, but in general in such methods one of these properties is sacrificed at the expense of the other, and both properties are rarely developed to a high degree in the same article.

It is therefore an object of the invention to provide a simple method of rolling magnesiumbase alloys which produces in the rolled article the combination of both high strength and high ductility.

The invention depends upon the discovery that the desired properties are obtained when the magnesium-base alloy, heated to a. temperature of 300-900 F., is passed at least once through rolls adjusted to produce a reduction in thickness of the metal of at least 40 per cent per pass, and is then cooled to a temperature below 200 F.

In a preferred embodiment, the process of the invention consists in' forming a magnesium-base alloy intermediate product having a thickness between about 60 and about 900 per cent above the final thickness desired for the rolled product (i. e., between 1.6 and 10 times such final thickness), rolling the intermediate product to substantially final thickness while it is at a temperature between 300 and 900 F. at a rate of reduction in thickness of at least 40 per cent per pass through the rolls, and then cooling the rolled product rapidly to a temperature below The intermediate product may be formed to the requisite thickness prior to the high-reduction rolling step in any suitable manner. preparing relatively thick rolled articles, in which case the intermediate product will have a thickness of an inch or more, the latter is conveniently a cast or extruded slab. In the case of thinner final articles, the intermediate is usually 8. rolled sheet, ordinarily, though not necessarily, prepared by rolling a cast or extruded slab at a temperature in the range 400- 800 F. inconventional manner, and then an.-

erns' the total amount of reduction givenin the.

subsequent rolling operation, and for this reason should be controlled rather carefully within the limits of to 900 per cent above final thickness to obtain the advantages of the invention.

The intermediate product, after being formed as described, is heated to a temperature in the range 300-900 F., and is then rolled to substantially final thickness at a rate of reduction in thickness of at least 40 per cent per pass through the rolls, rates up to per cent being possible without cracking in the case of most alloys. Ordinarily, only one or two passes are required to reach the desired final thickness.

The optimum rolling temperature in the range 300-900 F. will, of course, depend somewhat upon the composition of the alloy being rolled, as well as upon the thickness of the product, the rate of reduction per pass, and the speed of rolling, but for any given alloy can easily be determined by simple trial. For instance, with alloys consisting of magnesium and at leastv 1.0 per cent of manganese, together with lesser proportions of other elements such as calcium or cerium, the optimum rolling temperature is in the range 400-900 FL, whereas with alloys consisting of magnesium, 2! to 8' per cent of aluminum, and lesser proportions of other elements, temperatures of 300 to 500 F. are preferred. In general at the higher reductions per pass within the range stated and at high rolling speeds, the optimum rolling temperature will be nearer the lower end of the temperature range given, whereas at lower reductions and rates, higher temperatures are required.

After being subjected to the rolling operation, the magnesium-base alloy article is cooled rapidly to a temperature below 200 F., usually to room temperature. For thin sheets, e. g., those having a, thickness less than 0.060 inch, simple air cooling suflices, provided the sheets are not stacked as rolled but are exposed to air on all sides. For thicker sheets, however, it is desirable to cool the metal to below 200 F. by water or oil quenching so as to'avoid too great an annealing eifect such as would occur if the metal were 1 cooled too slowly after the rolling.

The high-strength ductile sheet producedas,

the extremely high rates of reductionin thickness employed in the process described. In such instances, the rolled and cooled sheet from the process may be further subjected to one or more light finishing passes through rolls at a small rate of reductionper pass, i. e. not over 5 per cent, to rovide a smoother surface and to control the thickness within the allowed tolerance. Similar results may be obtained if the sheet formed by the high reduction rolling step is given one or two very rapid light passes before it is cooled to below 200 F. In either case, however, the amount of this final finishing rolling should be kept at a, minimum since any substantial working of the metal after the highreduction rolling tends to decrease the strength and ductility of the metal resulting from that step. i

The following examples will serve to illustrate the invention but are not to be construed as limiting its scope:

Example 1 A magnesium-base alloy containing 1.5 per cent manganese and 0.15 per cent calcium, the balance being substantially magnesium, was cast into an ingot and extruded into a slab 0.25 inch thick. This slab was then heated to a temperature of 800 F. and rolled to a thickness of 0.150 inch. The resulting intermediate sheet was then allowed to cool to a temperature of 600 F. and was passed at a rate of 600 feet per minute once through -inch rolls adjusted to produce a 60 per cent reduction in thickness per pass, after which it was cooled in air to room temperature. The sheet thus produced exhibited the following properties: Elongation in 2 inches, long. 18 per cent, trans. 17 per cent; yield strength, long. 23,000 pounds per square inch, trans. 24,000 pounds; tensile strength, long. 35,000 pounds per square inch, trans. 37,000 pounds.

. Example 2 The process of Example 1 was repeated except that the intermediate sheet was rolled at 800 t F. and at a rate of 365 feet per minute. The

properties of the sheet were: elongation, long. 15 per cent, trans. 17 per cent; yield strength, long. 24,000 pounds per square inch, trans. 26,000 pounds; tensile strength, long. 37,000 pounds per square inch, trans. 36,000 pounds.

Example 3 An intermediate sheet prepared as in Example 1 was passed at a rate of 550 feet per minute once through 10-inch rolls adjusted to produce an 80 per cent reduction in thickness per pass,

after which it was cooled in air to room temperature. The sheet thus roduced exhibited the following properties: Elongation in 2 inches, long, 16 per cent, trans. 16 per cent: yield strength, long. 25,000 pounds per square inch, trans. 29,000 pounds; tensile strength, long. 36,000 pounds per square inch, trans. 38,000. pounds.

Example 4 A magnesium-base alloy containing 6.0 per cent aluminum, 0.3 per cent manganese, and 0.7 per cent zinc, the balance being substantially magnesium, was cast and extruded into a slab 0.5 inch thick. This slab was then heated to a temperature of 700 F. and rolled to a thickness of 0.100 inch. The resulting intermediate sheet was then allowed to cool to a temperature of 400 F. and was passed at a rate of 100 feet per minute once through 8-inch rolls adjusted to produce a 40 per cent reduction in thickness per pass, after which it was cooled in air to room temperature. The sheet thus produced exhibited the following properties in the longitudinal direction: Elongation in 2 inches, 18.5 per cent; yield strength, 38,800 pounds per square inch; tensil strength 47,600 pounds per square inch.

. Example 5 A magnesium-base alloy containing 3.0 iper cent aluminum, 0.3 per cent manganese, and 0.7

per cent zinc, the balance being substantially magnesium, was cast into an ingot and extruded to form a slab 0.5 inch thick. This slab was then heated to a temperature of 800 F. and rolled to a thickness of 0.150 inch. The resulting sheet was then passed at a temperature of 300 F. at a rate of 100 feet per minute twice through rolls adjusted to produce a reduction or 40 per cent per pass, after which it was at once cooled to room temperature. The resulting sheet had the following properties in the longitudinal direction: Elongation in 2 inches, 16 per cent; yield strength 34,600 pounds per square inch; tensile strength 43,900 pounds per square inch.

I claim:

1. In a method of producing a rolled article from a magnesium-base alloy containing at least 85 per cent of magnesium and selected from the class consisting of alloys consisting essentially of magnesium and 2 to 8 ,per cent of aluminum and alloys consisting essentially of magnesium and at least 1.0 per cent by weight of manganese, wherein-the alloy is formed into a product having a thickness between about 60 and about 900' per cent above the desired final thickness and is then rolled to substantially final thickness while at a temperature between 300 and 900 F., after which it is cooled rapidly to a temperature below 200 F., the improvement which com- .prises conducting the rolling at a rate of reduction in thickness of the metal between about 40 and about per cent per pass through the rolls.

2. The process according to claim 1' wherein the magnesium-base alloy rolled is an alloy consisting essentially of magnesium and at least 1.0 per cent by weight of manganese, and wherein the article is rolled while at a temperature of 400-900 F.

3. The process according to claim 1 wherein the magnesium-base alloy rolled is an alloy consisting essentially of magnesium and 2 to 8 per cent of aluminum, and wherein the article is rolled at a temperature of 300-500 F.

4. In a method of producing a high-strength ductile rolled product from a magnesium-base alloy containing at least per cent of magnesium and selected from the class consisting of alloys consisting essentially of magnesium and 2 to 8 per cent of aluminum and alloys consisting essentially of magnesium and at least 1.0 per cent by weight of manganese, the steps which consist in forming a product having a thickness between about 60 and about 900 per cent above the desired final thickness, rolling the product to substantially final thickness while at a temperature between 300 and 900 F. at a rate of reduction in thickness between about 40 and about 80 per cent per pass through the rolls, and then cooling the rolled product rapidly to room temperature.

5. In a method oi producing a high-strength ductile rolled product from a magnesium-base alloy containing at least 85 per cent of magnesium and selected from the class consisting of alloys consisting essentially of magnesium and 2 in thickness between about 40 andiabout 80 per cent per pass through the rolls, cooling the rolled product rapidly to room temperature, and then subjecting the cooled article to at least one light finishing pass through rolls at a relatively small reduction in thickness per pass.

6. In a method of rolling a magnesium-base alloy containing at least 85 per cent of magnesium and selected from the class consisting of alloys consisting essentially of magnesium and 2 to 8 per cent of aluminum and alloys consisting essentially of magnesium and at least 1.0 per cent by weight of manganese to develop highstrength and ductility, the steps which consist in subjecting the alloy while at a temperature of 300-900 F. to at least one pass through rolls adapted to produce a reduction in thickness of between 40 and 80 per cent per pass, and then cooling the alloy to a temperature below 200 F.

JOHN C. MCDONALD. 

